Apparatus and method for mat protection of non-thermal plasma reactor

ABSTRACT

A non-thermal plasma reactor is provided. The non-thermal plasma reactor includes a plasma-generating substrate, a housing and a mat. The plasma-generating substrate has one or more flow paths for an exhaust gas. The housing has an inlet and an outlet. The mat retains the plasma-generating substrate in the housing such that the one or more flow paths are in fluid communication with the inlet and the outlet. A voltage is supplied to the plasma-generating substrate to generate a plasma field. An electrically insulating layer is disposed between the plasma-generating substrate and the housing for preventing an arc of electricity from the plasma-generating substrate and/or the voltage to the housing.

TECHNICAL FIELD

[0001] This application relates to non-thermal plasma reactors. Moreparticularly, this application relates to an apparatus and method forprotecting a retention material or mat in a plasma-generating substrateof a non-thermal plasma reactor.

BACKGROUND

[0002] The removal of nitrogen oxides (hereinafter NO_(x)) from theexhaust gases of internal combustion engines is required for cleaneroperating vehicles. Improvements in fuel efficiency are achieved byoperating at conditions with an excess of air than required forstoichiometric combustion (i.e., lean burn or rich conditions). Such“lean burn” conditions are commonly achieved in diesel engines and fourcycle engines. However when lean-burn conditions are employed, commonpollution reduction devices (e.g., three-way catalysts) are inefficientin the reduction of nitrogen oxides.

[0003] One approach to reduce nitrogen oxide pollutants in exhaust gasesof engines operating under lean-burn conditions has been to incorporatea non-thermal plasma reactors in the exhaust lines along in addition tothe standard three-way catalyst. Such reactors treat the exhaust gasesusing a non-thermal plasma field. The non-thermal plasma field is a highlocal electric field. The plasma converts NO to NO₂, the NO₂ must thenbe subsequently reduced by a selective catalyst. For example, anon-thermal plasma reactor is described in U.S. Pat. No. 6,139,694, thecontents of which are incorporated by reference herein.

[0004] Non-thermal plasma reactors include a non-thermalplasma-generating substrate (“substrate”) disposed within a housing. Thesubstrate includes a pair of dielectric plates spaced from one anotherto form an exhaust gas flow channel. Preferably, the dielectric platesare non-conductive materials such as quartz, glass, alumina, mullite,and oxide free ceramics (e.g., silicon nitrite, boron nitrite, aluminumnitrite). A voltage supply is connected to a pair of electrodes on eachdielectric plate for providing a voltage between the dielectric platesin order to generate the plasma field in the flow channel between theplates. The exhaust gas flows through the flow channel, exposing the gasto the plasma field. The plasma field converts NO_(x) into eitherindividual elemental diatoms O₂ and N₂ and/or nitrogen dioxide NO₂.

[0005] The flow channels in the reactor are preferably long, narrowrectangular gas channels. However, such long, narrow substrates areprone to crushing due the forces necessary to restrain the substrate inthe housing. The plates of the substrate are also prone to arcing ofvoltage from the plates to the housing. Moreover, the substrate issubject to heating and cooling cycles, which places an additional strainon the substrate. These factors and others create obstacles with respectto retaining the substrate in the reactor.

SUMMARY

[0006] A non-thernal plasma reactor having a plasma-generatingsubstrate, a housing and a mat is provided. The plasma-generatingsubstrate has one or more flow paths for an exhaust gas. The housing hasan inlet and an outlet. The mat retains the plasma-generating substratein the housing such that the one or more flow paths are in fluidcommunication with the inlet and the outlet. A voltage is supplied tothe plasma-generating substrate to generate a plasma field. Anelectrically insulating layer is disposed between the plasma-generatingsubstrate and the housing for preventing an arc of electricity from theplasma-generating substrate and/or the voltage to the housing.

[0007] A non-thermal plasma reactor having a plasma-generatingsubstrate, a housing, a mat and a retaining device is provided. Theplasma-generating substrate has one or more flow paths for an exhaustgas. The housing has an inlet and an outlet. The mat retains theplasma-generating substrate in the housing such that the one or moreflow paths are in fluid communication with the inlet and the outlet. Avoltage is supplied to the plasma-generating substrate to generate aplasma field. The retaining device diffuses the exhaust gas away fromthe mat.

[0008] A method of forming a non-thermal plasma reactor is provided. Themethod includes providing a plasma-generating substrate, disposing theplasma-generating substrate in a housing, retaining theplasma-generating substrate in the housing with a mat, and supplying avoltage to the plasma-generating substrate for generating a plasmafield. The plasma-generating substrate has one or more flow paths for anexhaust gas. The plasma-generating substrate is disposed in the housingsuch that the one or more flow paths are in fluid communication with theinlet and the outlet. The retaining device diffuses the exhaust gas awayfrom the mat, distributes a low retention force of the mat to a weakside of the plasma-generating substrate, and distributes a highretention force of the mat to a medium strength area, a high strengtharea of the plasma-generating substrate, and to the areas where gasseals are required.

[0009] The above-described and other features and advantages of thepresent invention will be appreciated and understood by those skilled inthe art from the following detailed description, drawings, and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a side exploded view of an exemplary embodiment of anon-thermal plasma reactor;

[0011]FIG. 2 is a front view of the non-thermal plasma reactor of FIG.1;

[0012]FIG. 3 is a perspective view of a substrate of a non-thermalplasma reactor;

[0013]FIG. 4 is a cross sectional view of an exemplary embodiment of aretaining device for a non-thermal plasma reactor;

[0014]FIG. 5 is a view along lines 5-5 of FIG. 4;

[0015]FIG. 6 is cross sectional view of an alternate exemplaryembodiment of the non-thermal plasma reactor using the retaining deviceof FIG. 4;

[0016]FIG. 7 is a cross sectional view of another exemplary embodimentof a retaining device for a non-thermal plasma reactor;

[0017]FIG. 8 is a cross sectional view along lines 8-8 of FIG. 7;

[0018]FIG. 9 is a cross sectional view of another exemplary embodimentof a retaining device for a non-thermal plasma reactor;

[0019]FIG. 10 is a cross sectional view along lines 10-10 of FIG. 9;

[0020]FIG. 11 is a view along lines 11-11 of FIG. 9;

[0021]FIG. 12 is a cross sectional view of another exemplary embodimentof a retaining device for a non-thermal plasma reactor;

[0022]FIG. 13 is a cross sectional view of another exemplary embodimentof a retaining device for a non-thermal plasma reactor;

[0023]FIG. 14 is a cross sectional view of an alternate embodiment ofthe retaining device of FIG. 13;

[0024]FIG. 15 is a cross sectional view of another exemplary embodimentof a retaining device for a non-thermal plasma reactor;

[0025]FIG. 16 is a cross sectional view of another exemplary embodimentof a retaining device for a non-thermal plasma reactor;

[0026]FIG. 17 is a cross sectional view along lines 17-17 of FIG. 16;and

[0027]FIG. 18 is an end view along lines 18-18 of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] Referring now to FIGS. 1 and 2, a non-thermal plasma reactor isshown generally at 10. Non-thermal plasma reactor 10 (reactor) includesa housing 12 illustrated as a pair of shells 13. As illustrated, housing12 is an elongated rectangle. However, it should be recognized thathousing 12 having alternate configurations, such as, but not limited toelongated circles are considered within the scope of this application.Reactor 10 includes a retention material or mat 16 and a substrate 18.Mat 16 is adapted to retain substrate 18 in housing 12. Preferably,housing 12 is made of material capable of withstanding the hightemperature, high corrosive working environment of reactor 10. Forexample, housing 12 is made of metal, such as stainless steel.

[0029] Substrate 18 and housing 12 have a rectangular cross section.Preferably, substrate 12 is wrapped with mat 16 and is placed betweenshells 13. Shells 13 are connected to one another securing substrate 18therein. As illustrated in FIG. 1, reactor 10 includes a voltage port 20and a ground 24. Voltage port 20 supplies high voltage electricity tosubstrate 18.

[0030] It should be recognized that housing 12, mat 16 and substrate 18are described above by way of example only as having two-piececonstruction and rectangular cross-sections. However, any combination ofmultiple piece construction and corresponding cross sections areconsidered within the scope of the present invention.

[0031] Substrate 18 includes an inked or electrically active area 21.Mat 16 forms an interference-fit with housing 12 to hold substrate 18 inplace and provides adequate spacing, typically a minimum of 19 mm, toisolate the housing from electrically active area 21 of the substrate toprevent electrical arcing. Moreover, voltage port 20, being closer tohousing 12 than electrically active area 21, is also electricallyisolated.

[0032] Mat 16 fills the area between housing 12 and substrate 18, andretains the substrate in the housing. Preferably, mat 16 is acompressible fiber material and is made of a high temperature resistiveceramic fiber material, preferably comprising alumina. Mat 16 is adaptedto absorb the thermal expansion and compression of substrate 18, whichis in the range of about 7×10⁻⁶ mm per degree Celsius. For example, mat16 is 1100 HT supplied by 3M Company, which is capable of withstandingthe temperature environment within reactor 10 and is capable ofretaining substrate 18 throughout the expansion and contraction of thesubstrate.

[0033] Mat 16 erodes when exposed to the exhaust gas and becomescontaminated with a build-up of carbon from the exhaust gas. Sincecarbon is electrically conductive, carbon build-up on mat 16 creates anelectrical pathway between substrate 18 and housing 12 that interfereswith proper operation of reactor 10. Arcing due to carbon build-up isespecially problematic at voltage port 20 where spacing is diminished.

[0034] Substrate 18 is described with reference to FIG. 3. Substrate 18includes a plurality of ceramic plates 34, disposed in a spaced relationto form long rectangular cells or openings 36. Preferably, openings 36between plates 34 are maintained by spacers 38, which serve as verticalsupport for substrate 18. In use, exhaust gas is directed into openings36 and high voltage electricity is applied to each plate 34 to generatethe non-thermal plasma necessary to convert NO_(x) into eitherindividual elemental diatoms O₂ and N₂ and/or nitrogen dioxide NO₂.

[0035] Long rectangular cells or openings 36 create structurally weakzones or areas 40 in substrate 18. Areas 40 can only withstand lowcompression forces and makes the substrate 18 prone to crushing in theseweak areas if larger forces are encountered. For example, where plates34 have a thickness of about 1.5 mm a force of about 6 psi to about 17psi in weak area 40 may damage substrate 18.

[0036] Substrate 18 also includes medium strength areas 42 and highstrength areas 44, namely the portions of plates 34 supported by spacers38. The varying strength of areas 40, 42 and 44 affects how substrate 18is retained in the housing 12.

[0037] The retaining devices described below are adapted to provide highaxial compression of mat 16 at medium strength areas 42 and highstrength areas 44, but the low radial compression at low strength areas40.

[0038] Referring now to the embodiment of FIGS. 4 and 5, substrate 18 isfurther retained in housing 12 by a retaining device 50 such thatopenings 36 of the substrate are adjacent inlet 15 and outlet 17.Retaining device 50 is adapted to reduce the exposure of mat 16 toexhaust gas. Thus, retaining device 50 reduces the build-up of carbon onmat 16. Retaining device 50 is an enhanced diffusion header 52 disposedat inlet 15 and outlet 17 of housing 12. More specifically, header 52has an inside end 54 that is in close proximity to opening 36 ofsubstrate 18. Preferably, inside end 54 is in a range of about 0.5 mm to1.5 mm from substrate 18. More preferably, inside end 54 is about 1 mmfrom substrate 18. Header 52 causes the exhaust gas to expand withoutenergy loss and uniformly flow through substrate 18. Thus, header 52 actas a diffuser to direct the flow of exhaust gas into opening 36 and tominimize the amount of exhaust gas that contacts mat 16. Moreover,retaining device 50 more effectively distributes the compression forcesfrom the mat to substrate 18.

[0039] An alternate embodiment of non-thermal plasma reactor 10 isillustrated by way of example in FIG. 6 using retaining device 50.Reactor 10 further includes an insulating layer 28 disposed betweenhousing 12 and substrate 18. As discussed above, substrate 18 is held inhousing 12 with adequate spacing, to isolate the housing and thesubstrate to prevent electrical arcing. Insulating layer 28 furtherinsulates electrically active area 19 and voltage port 20 from housing12 such that the spacing between the housing and the substrate isreduced to about 6 mm to 9 mm. Accordingly, a reduction in size and costof reactor 10 is achieved through the use of insulating layer 28.Preferably, layer 28 is a layer of mica or other electrically insulatingmaterial. In one embodiment layer 28 is placed between housing 12 andsubstrate 18 during assembly. In alternate embodiments layer 28 issprayed, printed or the like onto housing 12 and/or substrate 18 priorto assembly of reactor 10.

[0040] Referring now to the embodiment of FIGS. 7 and 8, substrate 18 isfurther retained in housing 12 by a retaining device 60 such thatopenings 36 of the substrate are adjacent inlet 15 and outlet 17.Retaining device 60 is also adapted to reduce the exposure of mat 16 toexhaust gas. Retaining device 60 is formed by end 14 of housing 12. Morespecifically, housing 12 is dimensioned with respect to substrate 18such that end 14 is in close proximity to opening 36 of substrate 18.Preferably, end 14 is in a range of about 0.5 mm to 1.5 mm fromsubstrate 18. More preferably, end 14 is about 1 mm from substrate 18.Thus, end 14 acts as a diffuser to direct the flow of exhaust gas intoopening 36 and to minimize the amount of exhaust gas that contacts mat16. Moreover, retaining device 60 more effectively distributes thecompression forces from the mat to substrate 18.

[0041] Referring now to the embodiment of FIGS. 9-11, substrate 18 isfurther retained in housing 12 by a retaining device 70 such thatopenings 36 of the substrate are adjacent inlet 15 and outlet 17.Retaining device 70 is an overlap seal ring 72. More specifically, sealring 72 is sealed between housing 12 and ends 14. Preferably, seal ring72 is positioned in a range of about 0.5 mm to 1.5 mm from substrate 18.More preferably, seal ring 72 is about 1 mm from substrate 18. Thus,seal ring 72 acts as a diffuser to direct the flow of exhaust gas intoopening 36 and to minimize the amount of exhaust gas that contacts mat16. It is necessary because the mat adjacent to area 40 must have a lowdensity, less than 0.3 grams/cc to avoid excessive force on area 40.However, at this low density mat 16 is subject to erosion from theexhaust gasses, if unprotected. Moreover, retaining device 70 moreeffectively distributes the compression forces from mat 16 to substrate18.

[0042] Referring now to the embodiment of FIG. 12, substrate 18 isfurther retained in housing 12 by a retaining device 80. Retainingdevice 80 is an extension 19 of the peripheral edges of the outerceramic plates 34 of substrate 18. Extensions 19 are in close proximityto ends 14 of housing 12 to diffuse the flow of exhaust gas into opening36. Preferably, extensions 19 are positioned in a range of about 0.5 mmto 1.5 mm from end 14 and extend from substrate 18 by about 5 mm to 10mm. More preferably, extensions 19 are about 1 mm from ends 14 andextend from substrate 18 by about 7.5 mm. Accordingly, the closeproximity of extensions 19 and end 14 minimizes the amount of exhaustgas that contacts mat 16. In order to further reduce the exposure ofexhaust gas to mat 16 at retaining device 80, the mat at the interfaceof extensions 19 and ends 14 is coated with a sealant 82. Sealant 82 isadapted to seal mat 16 such that exhaust gases do not pass through thespace between extensions 19 and ends 14. In a preferred embodiment,sealant 82 is mat 16 compressed to a density above 0.3 grams/cc byplacing the mat between the end plate 14 and extension 19 duringassembly of reactor 10. It should be noted that use of sealant 82 in theform of mat 16 compressed to a density above 0.3 grams/cc is alsoavailable for the embodiment of FIGS. 7 and 8 described above.

[0043] Referring now to the embodiments illustrated in FIGS. 13 and 14,substrate 18 is further retained in housing 12 by a retaining device 90.Retaining device 90 reduces the exposure of mat 16 to exhaust gas andmore effectively distributes the compression forces from the mat tosubstrate 18. Retaining device 90 is a compression stop 92. Retainingstop 92 compresses mat 16 to a density greater than 0.3 gram/cc betweenthe retaining stop and end plate 14 without applying the relatively highforces generated by this compression to area 40. Thus, mat 16 has adensity less than 0.3 grams/cc, while the mat between stop 92 and endplate 14 has a density greater than 0.3 gram/cc for high erosionresistance. Stop 92 has an overlap portion 94 that overlaps substrate 18at openings 36 to distribute the axial compressive load to areas 42 and44 of the substrate. Preferably, stop 92 includes one or morereinforcing ribs 96. Reinforcing ribs help to transmit radialcompressive loading on weak zones 40 of substrate 18 to areas 42 and 44by preventing the stop from bending toward the substrate, and to preventstop 92 from bending due to the high compressive loads from mat 16between stop 92 and end plate 14.

[0044] Ends 14 include an enhanced diffusion header 98 disposed at inlet15 and outlet 17 of housing 12. More specifically, header 98 is in closeproximity to overlap 94. Preferably, header 98 is in a range of about0.5 mm to 1.5 mm from overlap 94. More preferably, header 98 is about 1mm from overlap 94. Thus, header 98 and stop 92 act as a diffuser todirect the flow of exhaust gas into opening 36 and to minimize theamount of exhaust gas that contacts mat 16. Mat 16 in this area is alsocompressed to a high density so it is resistant to erosion. Thus, stops92 avoid placing the high compressive loads from mat 16 on weak areas40. Moreover, the cooperation of overlap 94 and ribs 96 with substrate18 more evenly distributes the axial and radial compression from mat 16to areas 42 and 44 of substrate 18. In the embodiment of FIG. 14, stops92 are formed as separate pieces. Conversely, in the embodiment of FIG.15 stops 92 are formed as a single piece.

[0045] Referring now to the embodiment of FIG. 15, substrate 18 isfurther retained in housing 12 by a retaining device 100. Retainingdevice 100 includes an enhanced diffusion header 102 disposed at inlet15 and outlet 17 of housing 12 and a retaining ring 104 disposed betweenthe housing and ends 14. More specifically, header 102 has an inside end106 that is in close proximity to opening 36 of substrate 18.Preferably, inside end 106 is in a range of about 0.5 mm to 1.5 mm fromopening 36. More preferably, inside end 106 is about 1 mm from opening36. Header 102 causes the exhaust gas to expand without energy loss anduniformly flow through substrate 18. Retaining ring 104 compresses mat16 to a high density between the retaining ring and end plate 14 withoutapplying the forces from this compression to weak area 40. Accordingly,mat 16 adjacent to inside end 106 is highly resistant to erosion. Forpurposes of clarity retaining ring 104 is shown only at inlet opening15. However, it is considered within the scope of the present inventionfor retaining ring 104 to be used at outlet opening 17, and/or at bothinlet opening 15 and outlet opening 17. Thus, retaining ring 104 furtherminimizes the amount of exhaust gas that contacts mat 16. Morespecifically, retaining ring 104 is in close proximity to substrate 18.Preferably, retaining ring 104 is in a range of about 0.5 mm to 1.5 mmfrom substrate 18. More preferably, retaining ring is about 1 mm fromsubstrate 18. Thus, header 102 and retaining ring 104 act to diffuserthe flow of exhaust gas into opening 36 and to minimize the amount ofexhaust gas that contacts mat 16.

[0046] It should be noted that insulating layer 28 and sealant 82 aredescribed above by way of example as being used with retaining devices50 and 80, respectively. However, it is considered within the scope ofthe present invention for such insulating layers and sealants to be usedwith any of the retaining devices described herein.

[0047] Referring now to the embodiment of FIGS. 16-18, substrate 18 isfurther retained in housing 12 by a retaining device 106. Retainingdevice 106 is a rigid insulation board disposed areas 40 of substrate18. Thus, retaining device 106 minimizes forces on areas 40, andprovides a “stop” for mat 16 used at each end of substrate 18. Thus,retaining device 106, compresses mat 16 to a density above 0.3 grams/ccby placing the mat between the end plate 14 and the retaining deviceduring assembly of reactor 10. Accordingly, retaining device 106provides sealant 82 to further protect mat 16.

[0048] While preferred embodiments have been shown and described,various modifications and substitutions may be made thereto withoutdeparting from the spirit and scope of the invention. Accordingly, it isto be understood that the present invention has been described by way ofillustration only, and such illustrations and embodiments as have beendisclosed herein are not to be construed as limiting to the claims.

1. A non-thermal plasma reactor, comprising: a plasma-generatingsubstrate having one or more flow paths for an exhaust gas; a housinghaving an inlet and an outlet; a mat retaining said plasma-generatingsubstrate in said housing such that said one or more flow paths are influid communication with said inlet and said outlet; a voltage suppliedto said plasma-generating substrate for generating a plasma field; andan electrically insulating layer disposed between said plasma-generatingsubstrate and said housing for preventing an arc of electricity fromsaid plasma-generating substrate and/or said voltage to said housing. 2.The non-thermal plasma reactor of claim 1, further comprising aretaining device for diffusing said exhaust gas to saidplasma-generating substrate and away from said mat.
 3. The non-thermalplasma reactor of claim 1, wherein said retaining device distributes alow retention force of said mat to a weak side of said plasma-generatingsubstrate, and an high retention force of said mat to a medium strengtharea and a high strength area of said plasma-generating substrate. 4.The non-thermal plasma reactor of claim 3, wherein said low retentionforce compresses said mat to a density of less than 0.3 gm/cc and saidhigh retention force compress said mat to a density of more than 0.3gm/cc.
 5. The non-thermal plasma reactor of claim 1, wherein saidinsulating layer is a mica layer.
 6. The non-thermal plasma reactor ofclaim 2, wherein said retaining device is an enhanced diffusion headerof said inlet and said outlet in close proximity to said one or moreflow paths.
 7. The non-thermal plasma reactor of claim 6, wherein saidenhanced diffusion header is about 0.5 mm to 1.5 mm from said one ormore flow paths.
 8. The non-thermal plasma reactor of claim 2, whereinsaid retaining device is formed by said inlet and said outlet being inclose proximity to said one or more flow paths.
 9. The non-thermalplasma reactor of claim 8, wherein said inlet and said outlet are about0.5 mm to 1.5 mm from said one or more flow paths.
 10. The non-thermalplasma reactor of claim 8, wherein said plasma-generating substrateincludes peripheral extensions in close proximity to said inlet and saidoutlet.
 11. The non-thermal plasma reactor of claim 2, furthercomprising a sealant on said mat at least at an interface of saidretaining device and said plasma-generating substrate.
 12. Thenon-thermal plasma reactor of claim 2, wherein said retaining device isa seal ring that diffuses said exhaust gas into said one or more flowpaths and away from said mat.
 13. A non-thermal plasma reactor,comprising: a plasma-generating substrate having one or more flow pathsfor an exhaust gas; a housing having an inlet and an outlet; a matretaining said plasma-generating substrate in said housing such thatsaid one or more flow paths are in fluid communication with said inletand said outlet; a voltage supplied to said plasma-generating substratefor generating a plasma field; and a retaining device for diffusing saidexhaust gas to said plasma-generating substrate and away from said mat.14. The non-thermal plasma reactor of claim 13, further comprising anelectrically insulating layer disposed between said plasma-generatingsubstrate and said housing for preventing an arc of electricity fromsaid plasma-generating substrate and/or said voltage to said housing.15. The non-thermal plasma reactor of claim 13, wherein said retainingdevice distributes a low retention force of said mat to a weak side ofsaid plasma-generating substrate, and a high retention force of said matto a medium strength area and a high strength area of saidplasma-generating substrate.
 16. The non-thermal plasma reactor of claim15, wherein said low retention force compresses said mat to a density ofless than 0.3 gm/cc and said high retention force compress said mat to adensity of more than 0.3 gm/cc.
 17. The non-thermal plasma reactor ofclaim 13, wherein said insulating layer is a mica layer.
 18. Thenon-thermal plasma reactor of claim 13, wherein said retaining device isan enhanced diffusion header of said inlet and said outlet in closeproximity to said one or more flow paths.
 19. The non-thermal plasmareactor of claim 13, wherein said retaining device is formed by saidinlet and said outlet being in close proximity to said one or more flowpaths.
 20. The non-thermal plasma reactor of claim 13, wherein saidplasma-generating substrate includes peripheral extensions forming saidretaining device.
 21. A method of forming a non-thermal plasma reactor,comprising: providing a plasma-generating substrate having one or moreflow paths for an exhaust gas; disposing said plasma-generatingsubstrate in a housing having an inlet and an outlet such that said oneor more flow paths are in fluid communication with said inlet and saidoutlet; retaining said plasma-generating substrate in said housing witha mat and a retaining device; and supplying a voltage to saidplasma-generating substrate for generating a plasma field, wherein saidretaining device diffuses said exhaust gas to said plasma-generatingsubstrate and away from said mat, distributes a low retention force ofsaid mat to a weak side of said plasma-generating substrate, anddistributes an high retention force of said mat to a medium strengtharea and a high strength area of said plasma-generating substrate. 22.The method of forming a non-thermal plasma reactor of claim 21, furthercomprising providing an electrically insulating layer between saidplasma-generating substrate and said housing for preventing an arc ofelectricity from said plasma-generating substrate and/or said voltage tosaid housing.
 23. The method of forming a non-thermal plasma reactor ofclaim 21, wherein said low retention force compresses said mat to adensity of less than 0.3 gm/cc and said high retention force compresssaid mat to a density of more than 0.3 gm/cc.
 24. The method of forminga non-thermal plasma reactor of claim 21, wherein said insulating layeris a mica layer.
 25. The method of forming a non-thermal plasma reactorof claim 21, wherein said retaining device is an enhanced diffusionheader of said inlet and said outlet in close proximity to said one ormore flow paths.
 26. The method of forming a non-thermal plasma reactorof claim 21, further comprising forming said retaining device bypositioning said inlet and said outlet in close proximity to said one ormore flow paths.
 27. The method of forming a non-thermal plasma reactorof claim 21, further comprising providing peripheral extensions on saidplasma-generating substrate in close proximity to said inlet and saidoutlet.
 28. The method of forming a non-thermal plasma reactor of claim21, further comprising providing a sealant on said mat at least at aninterface of said retaining device and said plasma-generating substrate.29. The method of forming a non-thermal plasma reactor of claim 21,further comprising: compressing said mat to a high density between saidretaining device and said inlet opening and said outlet opening.
 30. Themethod of forming a non-thermal plasma reactor of claim 21, furthercomprising: placing a rigid insulation board proximate said weak side ofsaid plasma-generating substrate prior to disposing saidplasma-generating substrate in said housing, retaining saidplasma-generating substrate in said housing compressing said mat withsaid rigid insulation board to form a seal.